It is common practice in the conveying arts to drive a load-carrying, endless belt or chain belt by providing torque to one of the end rollers which supports the belt and defines its path. Traditionally, this mode of torque input has been accomplished by coupling an externally mounted electric or fluid motor to one shaft of the end roller, either directly or by a power transfer means such as a chain and sprockets.
This use of external hardware, however, is often undesirable for several reasons: From a safety standpoint, this external power arrangement presents the obvious hazards associated with rotating shafts, sprockets and chains. Furthermore, if electric powered, the potential for electric shock exists. From a sanitation point of view, it is necessary to keep the drive hardware from contaminating the conveyed product. This is a serious challenge for hydraulic powered conveyors, especially in the food processing industry. Likewise, the drive hardware must also be sanitizeable which presents additional challenges and costs. A further drawback to externally powered conveyors is the physical space requirement for the drive machinery. In many factories, such as those aboard vessels, space is very limited.
Accordingly, attempts have been made to provide a powered conveyor roller with an internal drive means. U.S. Pat. No. 3,376,758, issued to MacKay, is typical of the numerous electric motor driven disclosures. While providing a space-saving and sanitary solution, these electric powered rollers still represent a potential shock hazzard. Furthermore, in most applications, a costly gear reduction system must be included in the roller to achieve a usable belt speed. To provide a variable belt speed with this system requires an additional, expensive electrical control system such as a frequency controller. Moreover, in higher load applications, some provision must be made to remove the heat dissipated within the roller by the electric motor. Cooling means such as by forced air result in additional costs and require the abandonment of a hermetically sealed system.
The advantages of hydraulic motors; high power in a small package, easily varied speed and removal of dissipated heat with return oil flow, lend themselves quite readily to an internally powered conveyor roller. U.S. Pat. No. 4,013,166, issued to Weady et al., discloses an arrangement that appears similar to the present invention yet has quite serious disadvantages. Chief among these disadvantages are the large number of parts and high number of machining operations required to produce the roller. Four ball-bearing assemblies are employed along with the numerous attendant parts that must be machined to quite close tolerances. Moreover, in applications wherein the roller length is substantially longer than the internal hydraulic motor, the Weady design exhibits a significant disadvantage relative to the present invention; both shafts must span the full distance from the hydraulic motor through the endplates. All these factors contribute to a roller that is very expensive to produce. Disassembly is also quite complicated due to the high number of parts and bearings, resulting in high maintainence costs.
The motorized conveyor roller disclosed in U.S. Pat. No. 4,082,180, issued to Chung, suffers from the above mentioned dissadvantages of electric-motor powered rollers: potential for electric shock, the need for expensive gear reduction, and cooling difficulties. It is stated that the Chung design is only intended for relatively small conveyors and it is obvious that heat build-up would be a major problem at even modest horsepower ratings. Furthermore, like the Weady design, the Chung roller is not readily adaptable to rollers longer than the internal motor.